Data traffic over existing data networks is growing at a tremendous rate. One of the current issues facing network operators is how to efficiently use network resources. One popular type of network is a synchronous optical network (SONET) which is a well known network technology. Generally, SONET networks are organized as ring networks in which the nodes are connected in a closed loop configuration. Adjacent pairs of nodes are directly connected. Other pairs of nodes are indirectly connected with the data passing through one or more intermediate nodes. SONET rings utilized in telecommunication networks have traditionally utilized what is called 1+1 protection schemes. In such a scheme, there are two disjoint optical paths between every two nodes in the network. One path is the primary data path and the other path is the backup path which is only used if the primary path fails. Such a protection scheme allows for fast recovery in case of primary path failure. This fast recovery comes at a high price, however, in that 50% of the network resources go unused most of the time. As such, this is a fairly inefficient use of network resources.
As the result of the development of optical networking technology, other types of transport networks are being developed. In particular, the use of optical add-drop multiplexers (OADMs) and optical cross-connects (OXCs) in the optical transport layer now allow for Wavelength Division Multiplexed (WDM) optical mesh networks, in which network routers are connected directly to a switched optical core transport network consisting of OXC switches interconnected via high-speed Dense WDM (DWDM) line systems. As opposed to a ring network, in a mesh topology, each node may be directly connected to one or more (or all) others nodes. Thus, the topology of such a network resembles a mesh.
One benefit of a mesh network is its ability to share optical paths among multiple bandwidth demands. One such sharing scenario arises in the context of link failure protection schemes. In a mesh network, it is possible for two or more primary paths to share one backup path. Thus, for example, two primary data paths could share one backup path, thus making better use of network resources. In such a scheme, only approximately 33% of the network resources go unused (until a backup path is needed). More than two primary data paths could share one backup path, thus further increasing the efficiency of the network resources. Of course, this higher efficiency comes at the cost of being unable to provide a backup path in the event more than one primary path fails.
Another path sharing scenario arises in the context of bursty traffic. As is well known, internet traffic tends to be bursty with long periods of low traffic followed by sudden surges of high traffic. In such cases, it is preferable to share an optical path among multiple traffic flows. A recently proposed technique in this area is called optical burst switching, and has been proposed as a way to better utilize high capacity optical links amongst multiple IP traffic channels. The basic idea behind optical burst switching is as follows. Multiple demands share a primary path, but only one of the demands can be transmitted at any given time over the shared path. The source nodes for the traffic store the data packets in a memory buffer, and when a sufficient amount of data (i.e., “burst”) has accumulated for a demand, the shared path is allocated to, and used by, that demand. Once the burst has been received at the destination, the path becomes available for other demands.
The allocation of shared data paths must occur quickly in today's high speed networks. For example, in the restoration scenario, a failed link must be restored within 50 ms. This limit is generally imposed by telephony services, which require a restore time of 50 ms or less so that any delay would be imperceptible to users. In the optical burst switching scenario, any delay in the allocation of the shared link would result in an underutilization of the shared link and the possible dropping of data packets.
Where the events triggering the allocation of a shared data path are predictable, it is possible to implement an efficient sharing scheme using scheduling and time-division-multiplexing. However, in practice, most shared data path scenarios are not predictable. For example, in the context of optical burst switching, it is not possible to predict when traffic flow will hit a peak for any given data source. Similarly, in the context of failure restoration, it is not possible to determine when a network link will fail. This unpredictability, combined with the requirement of fast link allocation, makes it difficult to implement shared data paths in mesh networks. As will be described in further detail below in the detailed description, upon detection of a triggering event indicating the need for allocation of a shared data path, existing mesh networks need to be reconfigured in order to allocate the shared data path as necessary. This reconfiguration generally requires setting up the shared path by sending appropriate signaling commands to the mesh network components, thus instructing the components to reconfigure themselves as required. This reconfiguration via signaling has heretofore been unable to comply with the 50 ms timing constraint described above. As such, optical mesh networks have not replaced the more convention SONET rings. The 1+1 protection scheme of SONET networks allow such networks to provide the required fast restoration.
What is needed is a technique for allocating shared data paths in mesh networks so that the benefits of mesh networks may be realized in high speed data networks.